Endoplasmic reticulum stress has a profound effect on cancer cell proliferation and survival, and also has the capacity to activate cells of the adaptive immune system. Multimodality treatments that combine conventional cancer therapies with antigen-specific immunotherapy have emerged as promising approaches for the control of cancer. However, it is not well known whether ER stress inducing agents can influence the efficacy of tumor antigen targeted vaccines. We used previously developed therapeutic human papillomavirus (HPV) DNA vaccines encoding calreticulin (CRT) linked to HPV-16 E7 antigen (CRT/E7) vaccine and ER stress inducing agent, 3-bromopyruvate in a preclinical model for its potential to enhance E7-specific CD8+ T cell immune responses as well as antitumor effects against E7-expressing tumor (TC-1 cells). In vitro assay, luciferase-expressing TC-1 tumor cells were treated with 3-bromopyruvate. E7-specific CD8+ T cells were added to evaluate the cytotoxicity. The degree of cytotoxic T lymphocytes-mediated killing of the tumor cells was measured with the IVIS Luminescence Imaging System. We also determined the levels of ER stress markers in 3-bromopyruvate treated TC-1 cells. In vivo assay, TC-1 tumor-bearing mice were treated with 3-bromopyruvate (10mg/kg, intraperitoneal injection) and/or CRT/E7 DNA vaccine (30μg/mouse). The tumor mass size and survival were evaluated. Treatment of TC-1 cells with 3-bromopyruvate induced significant in vitro cytotoxicity. We found that treatment with 3-bromopyruvate led to upregulation of ER stress markers (CHOP, GRP78) in E7-expressing TC-1 tumor cells. More importantly, treatment with combination of 3-bromopyruvate and CRT/E7 DNA vaccine led to improved antigen-specific CD8+ T cell immune responses as well as therapeutic antitumor effects in TC-1 tumor-bearing mice. Thus, our data indicate that 3-bromopyruvate can enhance therapeutic HPV vaccine potency in generating improved antigen-specific immune responses and antitumor effects. These findings have important implications for future clinical translation.

Citation Format: Sung Yong Lee, JaeJeong Shim, Kang Kyung Ho, Kye Young Lee, Chien-Fu Hung, T.-C. Wu. Endoplasmic reticulum stress enhances the antigen-specific T cell immune responses and therapeutic antitumor effects generated by therapeutic HPV vaccines. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr B33.